The invention relates to seal means for sealing two substantially flat closing surfaces, respectively of two separable elements, said elements forming, when sealed, a boundary between a first space and a second space, in order to prevent a first gas at a first pressure, which is flowing in the first space, to exit through an interface that is still present between said two closing surfaces disposed one opposite to the other for sealing.
The invention further relates to such seal means for high temperature chemical vapor deposition chamber. The invention also relates to a chemical vapor deposition apparatus having a deposition chamber with such seal means.
The invention finds an application in the industry of vapor deposition apparatus for manufacturing semiconductor devices, for example, gallium arsenide semiconductor devices.
A support and seal structure for CCVD reactor is already known from U.S. Pat. No. 5,105,762. This document discloses a multi-chamber continuous chemical vapor deposition reactor. In the process chambers, the deposition process depends upon gas flow through the reactor. A semiconductor wafer is placed in a carrier and is moved successively through the various chambers and out the end of the reactor. The various chambers are separated by junction walls. Each process chamber has associated heat means for the wafer, gas inlets and outlets, a track on which the wafer carrier is moved and seal means to prevent the gas from escaping towards the environment outside the reactor, and to prevent exhaust gases from entering the process chambers. The seal means may be a pressure differential seal to prevent a gas from entering an area within the reactor or escaping the reactor at points other than the exhaust ports. Such a gas seal means may be formed between a process chamber wall and a junction wall. A process chamber wall is held against the junction wall by a clamp assembly made up of flange parts and bolts. The interface between the clamp and the process chamber wall is not a hermetic seal. An inert purge gas such as nitrogen N2 is introduced through a gas plenum formed through the junction wall towards the interface opening. The nitrogen N2 propagates into the interface opening in two directions. On the one hand, the nitrogen N2 flows out through a first part of the interface opening disposed between the flange and the process chamber wall in the direction of the outside of the reactor. On the other hand, the nitrogen N2 flows out in an opposite direction, through a second part of the interface opening disposed between the process chamber wall and the junction wall to an exhaust port towards an exhaust plenum located on the other side of the junction wall with respect to the process chamber wall. Reactive process gases such as Silane, H2, HCl are introduced into an inlet formed through the junction wall and flow into the reactor chamber over a susceptor for a wafer and out said exhaust port into said exhaust plenum. The pressure of the inert gas N2 introduced into the junction wall/chamber wall interface opening is greater than that of the reactive process gases introduced into the specific inlet so that the reactive process gases must flow into the reactor chamber, thus sealing the environment outside the reactor chamber from the reactive process gases. In particular, a part of the reactive process gases, which may tend to flow out through the first part of the interface opening towards the outside of the process chamber, is forced through an outlet, which is formed inside the junction wall and towards said exhaust plenum, by the counter-flow constituted by the inert gas N2.
So, in the known patent, the chamber wall is fixed to the junction wall using flanges and bolts thus defining a fixed interface in a high temperature area. The chamber and the junction walls are not movable the one with respect to the other in the strict meaning of the term. They are only apt to be dismantled. The high temperature seal means are not intended to be installed between movable elements. The inert gas, which is introduced in the same area of the junction wall as the reactive gases, prevents the flowing reactive gases from exiting through the so-called fixed interface by forming a counter-flow. The reactor apparatus comprises several small chambers that each receives only one wafer at a time. It is the wafer that is movable.
Problems occur when the process chamber is of great dimension in order to accommodate several wafers at the same time, and when a first element of said large process chamber must be movable with respect to a second element, for example, for opening/closing the process chamber for introducing the wafers. An other problem occurs when said movable elements are located in a high temperature area where the process reactive gases are flowed through the process chamber at high temperature.
Due to the location in a high temperature area, it is not possible to make use of standards seals to seal such first and second movable elements. Now, due to the great dimension of the process chamber, and in view of opening/closing the process chamber, a first closing surface formed as a flat portion of the first movable element is not allowed to be simply set in contact upon a corresponding second closing surface formed as a flat portion of the second movable element, because a sufficient degree of flatness of these large-dimensioned closing surfaces is not possibly mechanically obtained. The unavoidable closing interface would be irregular. So, such a way of closing the process chamber by simple contact of opposite closing surfaces, without sealing means, would let the flowing reactive gases exit through the unavoidable closing interface, or a counter-flow formed by an inert gas flowing through said closing interface would have an irregular flow and could not be regularly efficient. Usually, in chemical deposition process, the flowing process reactive gases that are used are very dangerous and polluting and may not be allowed to flow outside the process chamber but through the plenum exhaust.
An other problem, in chemical vapor deposition, is that the gas pressure inside the process chamber is not allowed to be substantially different from the atmospheric pressure value. So, the inert gas for forming a counter-flow may be introduced in a way that does not disturb the process pressure value, i. e. the amount of inert gas for forming an effective counter-flow may not be too important whichever the peripheral length of the movable elements of the process chamber. Too great an amount of inert gas to prevent the flowing reactive process gases from exiting the reactor chamber, may mix with, and dilute said gases, and may disturb the process performed inside the process chamber.
Also a problem, due to the fact that the inert gas is not allowed to disturb the process, is that the inert gas may not be introduce in the same area as the process gases because the odds that the inert gas and the process gases mix are too important.
So the problems of providing seal means for movable elements of a process chamber in a reactor, taking into account that the process chamber has great dimension and that the movable elements are located in high temperature area, typically more than 300xc2x0 C. (three hundred degree centigrade), the process being carried out using flowing reactive gas at low pressure value (substantially near the atmospheric pressure), is not solved by the disclosure of the known document.
It is a purpose of the invention to provide seal means for movably sealing two substantially flat closing surfaces, respectively of two movable elements, said elements forming, when sealed, a boundary between a first space and a second space, in order to prevent a first gas at a first pressure, which is flowing in the first space, to exit through an interface that is still present between said two closing surfaces disposed one opposite to the other for sealing.
It is a further purpose of the invention to provide a process chamber having seal means, to be applied to first and second closing surfaces of movable first and second elements of said process chamber, said elements forming, when sealed, a boundary between the process chamber, referred to as first space, and a second space surrounding said process chamber, to permit of moving said first and second elements the one with respect to the other to open or close the process chamber between process operations, said process operations taking place in the process chamber using flowing process gases at a predetermined gas pressure, while preventing said flowing process gases to exit the process chamber but through a specific exhaust port, and while keeping the flowing process gases in the process chamber under controlled pressure conditions during said process operations.
It is also a purpose of the invention to provide a process chamber for processing wafers using flowing process reactive gases at high temperatures and low gas pressure values, said process chamber having a first and a second separable elements, at least one inlet for the process reactive gases and having such seal means to allow said first and second separable elements to be strictly movable the one with respect to the other, for instance for opening and closing the process chamber between the process operations, while preventing the flowing process reactive gases from exiting the process chamber but through a specific exhaust port during the process operations.
It is a purpose of the invention to provide a reactor having such a process chamber with such seal means, said process chamber having first and second parts of dimension appropriate to receive several wafers at the same time.